Poly(Enaminonitriles): New Materials with Interesting Properties

Abstract

The thermal stability of polymers is influenced by both chemical and physical factors.^1,2 The chemical factors are primary bond strength, secondary or van der Waals’ bonding forces, hydrogen bonding, resonance stabilization, mechanism of bond cleavage, molecular symmetry, purity, crosslinking and branching. The physical factors include molecular weight, molecular weight distribution and crystallinity. The primary bond strength contributes the most to the thermal stability of polymers. The bond dissociation energy⁴ of a carbon - carbon single bond is 350 kJ/mol, and that of a carbon -carbon double bond is 610 kJ/mol. A double bond in an aromatic system is further strengthened by resonance stabilization, adding 164 to 287 kJ/mol to the bond dissociation energy. Almost all thermally stable polymers contains aromatic carbocyclic or heterocyclic rings. The bond dissociation energy of a carbon - fluorine bond of 430 kJ/mol is increased to 504 kJ/mol by a second fluorine atom attached to the same carbon atom. Therefore, perfluorinated materials are more thermally stable. Inorganic polymers which have inherent higher bond strengths (e.g. B-N, Si-N, Ti-O) are often susceptible to chemical attack such as hydrolysis. As a consequence, few useful polymers containing inorganic backbones have been developed.⁵